This invention relates to increasing the impact resistance in rubber-modified vinyl aromatic polymers and more particularly to the addition of small quantities of bromine-containing compounds to styrene polymers in order to enhance impact strength.
The desirability of producing higher impact resistant grades of styrene polymer is well known in the art. Compositions and methods have been developed which produce high impact polystyrene by the incorporation of a rubber-polystyrene discrete phase into a polystyrene matrix. Possible impact modifiers for styrene polymers include polybutadiene rubber (PBD), styrene-butadiene rubber (SBR) and ethylene-propylene-diene monomer rubber (EPDM). Such rubbers are found in concentrations from three to ten percent. There is a need for new techniques that increase the impact strength of various styrene based polymers. Especially, there is a need for a method of increasing the impact strength of EPDM-modified styrene polymers, since these polymers have inherently low impact strengths.
British Pat. No. 1,185,122 discloses the use of relatively high concentrations of .beta.-bromostyrene in rubber-modified polystyrene as a means to prepare a transparent polymer, however there is no mention of an enhancement of impact strength nor were EPDM rubbers used.